On a side note, forgive my ignorance, but what exactly was Japan doing in Manchuria in 1942?

Minign for war material mostly, But I think you mean 1924-1925. More or less, at that time, they were doing the same thing Britain was doing in Burma since about the 1820's. At that time it was a power vacuum between the Russians ( in their Civil War) and a weak Chinese republic. The Mukden incident pretext for invasion of Manchuria was in 1931 and led to establishment of the puppet ex-Ching Emperor PuYi as "leader" of Manchukuo.